Shellscript Interpreting

I am trying to interpret the following shellscript and am having a very difficult time. Could one of you Unix gurus pleasssseeee help me out? You just won't know how much of a life saver you would be for me.

PN=`basename "$0"`			# Program name
VER=`echo '$Revision: 1.2 $' | cut -d' ' -f2`

Usage () {
    echo "$PN - who is doing what, $VER (stv '95)
usage: $PN [-l] [-h] [user]
    -h: suppress the heading
    -l:	long form of output" >&2
    exit 1
}

Msg () {
    for i
    do echo "$PN: $i" >&2
    done
}

Fatal () { Msg "$@"; exit 1; }

LongOutput=no
Header=yes
while [ $# -gt 0 ]
do
    case "$1" in
	-l)	LongOutput=yes;;
	-h)	Header=no;;
	--)	shift; break;;
	-*)	Usage;;
	*)	break;;			# First file name
    esac
    shift
done

[ $# -gt 0 ] && User="$1"

if [ "$LongOutput" = no ]
then
    [ $Header = yes ] && {
	date
	uname -n
    }

    # Sample output of who:
    #	heiner   console Apr 26 08:18
    who |
	while read Name Tty Mon Day Time Host Rest
	do
	    [ -n "$User" -a "$User" != "$Name" ] && continue
	    echo "
$Tty	$Name	$Time"
	    case "$Tty" in
		*tty*)	T=`echo "$Tty" | sed -e 's:.*tty\(..\).*:\1:'`;;
		*)	T=`echo "$Tty" | sed -e 's:/dev/\(..\).*:\1:'`;;
	    esac

	    # Sample output of ps -c:
	    #	PID TT STAT  TIME COMMAND
	    #	327 p2 IW    0:19 ksh
	    ps -ct"$T" | tail +2 |
		while read pid tty stat time command
		do
		    echo "    $Tty	$pid	$time	$command"
		done
	done
else
    # Long form: use "w" output format
    if [ $Header = yes ]
    then FirstLine=1
    else FirstLine=3
    fi
    if [ -z "$User" ]
    then
	w
    else
	w | grep "$User"
    fi | tail +$FirstLine
fi

Thanks a million!!!!!!

added code tags for readability --oombera

Well, without going into a line by line
description, this script is apparently a
"whodo" script. Basically, it "maps" the logged
in userid's and tty's to specific processes,
hence "whodo" - "Who is doing what"

At least that's the way I read it

Thanks rwb1959 for replying. Unfortunately, that is just what I needed - a line by line description. I am trying to understand the various commands in Unix, but as I had stated I am having a terrible time doing it.

Thanks again.

Do you have an UNIX shell programming reference books? There is a tremendous value to reading the first few chapters on syntax, variables and other shell script constructs... .especially pipes and filters. Using chains of filters by 'piping' the output of one command into the input of another is a very powerful construct. When you understand this construct (the use of the little "|" pipe) your shell-life gets much easier.